The present invention relates to an apparatus for supplying fuel to a gas-generating system to generate a hydrogen-rich gas in a fuel cell system, the gas-generating system comprising two gas-generating components. Further, the present invention relates to a method for operating such an apparatus.
To operate fuel cells for mobile applications, hydrogen from a fuel, such as methanol, is generated in a gas-generating system by steam reforming and/or partial oxidation. For both processes, it is necessary to supply and meter the liquid reactants to the gas-generating components.
When operating a gas-generating system, it may be necessary to supply different gas-generating components consecutively with fuel. Usually, each gas-generating component has its own metering device for supplying and metering the fuel, which is separate from that of the other gas-generating components. It has proven to be a disadvantage that, when changing over or connecting the individual gas-generating components, a continuous metering and supplying of fuel to the individual gas-generating components is not assured.
Changing over or connecting the fuel supply from one gas-generating component to a different gas-generating component usually takes place by connecting a metering device of one gas-generating component to another gas-generating component that is to be switched over. The first gas-generating component can subsequently be switched off. This change between different operating states of the gas-generating system causes interference with the continuous metering and supplying of fuel to the gas-generating components. In addition, due to dead volumes, for example, there is interference with the continuous generation of hydrogen-rich gas in the gas-generating components for the downstream fuel cells. Accordingly, there is a drop in performance of the fuel cells.
It is an object of the present invention to provide an apparatus having a compact and inexpensive construction which allows change over between different operating states of the gas-generating system without a drop in performance of the downstream fuel cell. Further, it is an object of the present invention to provide a method for operating this apparatus.
For both gas-generating components, the apparatus according to the present invention has a common metering device, which supplies both gas-generating components with fuel over a valve-controlled distribution. In addition, a fuel storage basin is present. This fuel storage basin supplies fuel to a gas-generating component during the changeover or connecting process between gas-generating components.
Accordingly, it is possible, when changing over or connecting the individual gas-generating components, to ensure a continuous generation of hydrogen-rich gas for the downstream fuel cell. A drop in performance of the downstream fuel cell is prevented. The downstream fuel cell may be a PEM fuel cell with a proton-conducting electrolyte membrane.
It is a further advantage of the present invention that the inventive apparatus can be constructed compactly and inexpensively, since only a metering device is required for supplying fuel to the gas-generating components.
The fuel storage basin proves to be particularly advantageous with respect to good fuel metering to the gas-generating components.
In an embodiment of the present invention, the valve-controlled distribution is constructed in the following manner. A valve is connected between the metering device and the fuel storage basin; between the metering device and the first gas-generating component; between the metering device and the second gas-generating component; and between the fuel storage basin and the second gas-generating component.
Advantageously, the fuel storage basin can be filled with fuel before the gas-generating system is started and/or after it is switched off.
In an embodiment of the method according to the present invention, the first gas-generating component is changed over to or connected with the second gas-generating component by the following steps, starting by supplying fuel to the first gas-generating component by the metering device:                connecting the fuel storage basin to the second gas-generating component, so that both gas-generating components are supplied with fuel;        connecting the metering device to the second gas-generating component, so that both gas-generating components can be supplied simultaneously with fuel by the metering device, it being possible to supply the second gas-generating component additionally with fuel by the fuel storage basin;        disconnecting the fuel storage basin from the second gas-generating component, so that the two gas-generating components are supplied with fuel only by the metering device;        disconnecting the metering device from the first gas-generating component, so that only the second gas-generating component is supplied with fuel by the metering device.        
It is also possible to reverse the sequence of the two steps of the process mentioned last.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the present invention when considered in conjunction with the accompanying drawing.